Welding is used as a powerful manufacturing method for the high quality joining of metallic components in all branches of US industries. Respiratory effects, metal fume fever, cancer, and effects on kidneys, nervous system, reproductive system and skin have been associated with welding fume exposures. The recent census data indicate that over 800,000 workers in the United States are involved in welding or allied processes full time, while it is estimated that more than one million perform welding intermittently as part of their work expectations. Although there are many welding processes employed for various applications Manual Metal Arc (MMA) welding using hand-held electrodes and Metal Inert Gas (MIG) welding using continuous wire applied to mild steel, stainless steel, and aluminum yield combinations which are practiced by 70% of the welding population. We propose to determine the inhaled concentration of welding fume as a true measure of exposure associated with the MMA process. To date, welding fume exposure studies in field or, in a very limited extent, under laboratory conditions either assessed the area exposures or personal exposures in the breathing-zone of workers. Very few studies have evaluated fume concentration inside and outside of the welder helmet. However, no studies have attempted to quantitatively determine the inhaled concentration of welding fumes as a function of welding processing parameters such as base material/ electrode combination, welding current and voltage, and distance of the welder from the source area. The experimental design and data analysis outlined in this proposal addresses this critical data gap. The proposed experiments will be performed using a life-size head and shoulders of a manikin for which breathing will be simulated through the mouth using a ventilator pump. The tidal volumes and breathing frequencies will be adjusted to correspond to the characteristic values for men at rest or performing normal physical work. The manikin, wearing a welding helmet, will be exposed to MMA welding fumes in an exposure chamber during a series of experiments using a combination of welding and subject-related parameters. A filter cassette will be placed inside the mouth and welding fumes will be collected on 37-mm filters, which will be analyzed gravimetrically to determine the particulate mass and inhaled concentration. The ratio of inhaled concentration to total/respirable fume concentration outside of the helmet in the breathing-zone will also be estimated by concurrently sampling the air outside of the helmet using a 37-mm cassette and a BGI cyclone, respectively. A central composite experimental design with a number of quantitative and qualitative parameters will be used as a basis of experimental design in order to efficiently and systematically determine the most influential parameters affecting inhaled, total/respirable concentration of welding fumes. This is basically a quadratic empirical surface-response model to determine the relationship between inhaled concentration along with total /respirable fume concentration and influential welding parameters. These results will enhance our understanding of the inhaled dose of welding fumes, which serve as a better exposure metric for health effects studies. In addition, this study will provide necessary information for evaluating biological significance of welding fume personal or area exposure measurements and may provide insights into the biological relevance of the current exposure standard (TLV-TWA) for welding fumes.